1. Field of the Invention
The present invention relates to an apparatus capable of ejecting droplets, and a method for manufacturing the apparatus.
2. Description of Related Art
One type of ink-jet head in an ink-jet printer is formed by a passage unit and an actuator unit being put in layers. The passage unit includes therein ink passages each constituted by an ink tank, a pressure chamber, and a nozzle, etc. The actuator unit applies pressure to ink contained in the pressure chamber in the passage unit. As the passage unit, for example, a layered structure of plural metal plates made of 42% nickel alloy steel (42 alloy) may be adopted. As the actuator unit, for example, a layered structure of plural piezoelectric ceramic sheets in which individual electrodes and common electrodes always kept at the ground potential are alternately sandwiched between the piezoelectric sheets may be adopted. An electric field is in advance applied to regions sandwiched between the individual electrodes and the common electrodes in the actuator unit, to thereby produce active portions polarized in their thickness direction.
The passage unit and the actuator unit are bonded to each other with an adhesive or an adhesive sheet being interposed therebetween such that the above-mentioned active portions may face the pressure chambers in the passage unit. When a drive pulse signal is applied to the individual electrodes, portions of the actuator unit corresponding to the active portions deform to change the volume of the pressure chambers. Thereby, pressure is applied to ink that has been supplied from the ink tank into the pressure chambers, and then the ink is ejected from the nozzles.
When capacitance between the electrodes at the active portion of the actuator unit is large or when a high drive voltage is required for driving the actuator unit, a power consumption (which is proportional to a product of the capacitance and a square of the drive voltage) of a driver circuit for driving the actuator unit uneconomically becomes large. In such a case, heat generation in the driver circuit significantly increases, and hence troubles by heating may easily be caused. In order to prevent the troubles by heating, a relatively expensive driver must be used to disadvantageously raise the cost of an electric system. Moreover, a heat sink, which is attached to dissipate heat generated in the driver circuit, need be large in size, and accordingly a size of an apparatus as a whole is also increased. Further, when capacitance between the electrodes at the active portion of the actuator unit is large, a delay corresponding to a charge time of a capacitor arises to thereby exhibit a moderate change in voltage between the electrodes. Consequently, it becomes hard to drive the actuator unit in a desired manner.
Capacitance between electrodes at an active portion of an actuator unit can be reduced by decreasing areas of the electrodes, which however increases a drive voltage required for providing a desired deformation of the active portion. That is, capacitance and a drive voltage have a correlation that the larger one becomes, the smaller the other becomes. Accordingly, it is hard to optimize both of them at the same time in order to avoid the aforementioned problems.